1. Field of the Invention
The invention relates to a solenoid control device that executes feedback control such that a drive current for a solenoid follows a target current.
2. Discussion of Background
There is a solenoid control device that executes feedback control of a drive current for a solenoid, by driving, through pulse width modulation (PWM), a switching element provided on a power supply line to the solenoid. A solenoid control device described in Japanese Patent Application Publication No. 2012-13098 (JP 2012-13098 A) includes a current detection unit that detects a drive current (actual current) for a solenoid. The solenoid control device sets a target value of the drive current for the solenoid, and computes, in PWM control, a duty ratio at which there is no deviation between a current value detected by the current detection unit and the target value. Then, the solenoid control device drives the switching element through PWM, by transmitting a drive signal based on the duty ratio to a drive circuit. In this way, the solenoid control device executes feedback control of a drive current for the solenoid.
If a short-circuit occurs between both terminals of the solenoid in the solenoid control device, when the switching element is driven through PWM and is turned on, an overcurrent is generated. At this time, when the detected current value becomes larger than the target value, the solenoid control device reduces the duty ratio of the drive signal such that the detected current value becomes the target value. Thus, the drive current for the solenoid decreases to 0 amperes (A) or a value close to 0 A. Therefore, when the detected current value becomes smaller than the target value, the solenoid control device increases the duty ratio. Thus, an overcurrent is generated again. After that, a so-called hunting phenomenon occurs, that is, the drive current for the solenoid significantly fluctuates.
Previously, means for detecting an overcurrent, means for detecting a current abnormality, and the like have been proposed, and these detecting means detect an abnormality on the basis of presence of a steady abnormality, that is, on the basis of the fact that a state where a drive current for a solenoid is larger than or equal to a predetermined value continues. Therefore, with the conventional detecting means, it is not possible to appropriately detect a short-circuit between both terminals of the solenoid, which is accompanied by a hunting phenomenon. In order to take appropriate measures against a short-circuit between both terminals of the solenoid, a solenoid control device that is able to detect such an abnormality has been desired.